Recently, as vehicles and various electronic apparatuses have been more functional and diversified, a switch provided on a control panel of each of them often has an illumination knob. For confirming and recognizing the position of the switch even in a dark, the illumination knob is illuminated by a luminous source provided in the control panel.
A conventional illumination knob will be described with reference to FIG. 4 through FIG. 5B.
FIG. 4 is a sectional view of the conventional illumination knob. Knob section 1 made of insulating resin has a pair of elastic pawls 1C formed at a lower surface of knob section 1. Pawls 1C protrude downward and have recesses 1B on respective inner surfaces of the pawls. Knob section 1 has opening 1A provided in its upper surface. Holder 2 has a substantially cylindrical shape and is made of insulating resin. Holder 2 has a pair of protrusions 2A formed on its outer surface, and the recesses 2A are latched on recesses 1B. Thus, holder 2 is attached at a lower section of knob section 1. Display section 3A of an upper end of light-transmittable light guide unit 3 is inserted into opening 1A of knob section 1. Light guide unit 3 has a pair of protrusions 3B provided at a lower end of unit 3, and the protrusions 3B are latched in holes 2B of a lower end of holder 2. Therefore, light guide unit 3 is accommodated and fixed in holder 2, thus providing the illumination knob.
FIGS. 5A and 5B are exploded sectional views of the conventional illumination knob. As shown in FIG. 5A, light guide unit 3 is inserted into holder 2 from underneath of holder 2 in a direction A. Then protrusions 3B at the lower end of light guide unit 3 are latched in holes 2B, thus combining holder 2 with light guide unit 3.
Next, as shown in FIG. 5B, holder 2 having light guide unit 3 inserted therein is inserted into knob section 1 from underneath section 1 in a direction B, and elastic pawls 1C elastically deforms in right and left directions. Then, recesses 1B are latched on protrusions 2A by elastic restoring force of elastic pawls 1C, thus combining holder 2 with the lower section of knob section 1 to provide the illumination knob.
This illumination knob is mounted at the switch provided on the control panel. When the luminous element, such as a light bulb or a light emitting diode, in the control panel emits light the light is transmitted through light guide unit 3 and illuminates display section 3A inserted into opening 1A. This structure allows the position of knob section 1 to be confirmed and recognized even in a dark.
In the conventional illumination knob, knob section 1 holds holder 2 and light guide unit 3 with elastic pawls 1C. When display section 3A of an upper surface of knob section 1 is pressed by strong force in a direction C, the force is transmitted from light guide unit 3 to holder 2. The force may make elastic pawls 1C open in right and left directions, thus unlatching protrusions 2A from recesses 1B. As a result, holder 2 and light guide unit 3 may be fallen from knob section 1.
To prevent the falling, it is necessary to applying adhesive to recesses 1B and protrusions 2A or welding elastic pawls 1C of knob section 1 to holder 2. These operations make the illumination knob need a long time to manufacture and be expensive.
Another conventional illumination knob is disclosed in Japanese Patent Laid-Open Publication 8-207622.